1. Field of the Invention
The present invention generally relates to a semiconductor device and a method of forming the same. More specifically, the present invention relates to a semiconductor device including a DRAM capacitor with a bottom electrode having an improved adhesiveness with an adjacent insulating film.
2. Description of the Related Art
All patents, patent applications, patent publications, scientific articles, and the like, which will hereinafter be cited or identified in the present application, will hereby be incorporated by reference in their entirety in order to describe more fully the state of the art to which the present invention pertains.
A memory cell such as a DRAM (Dynamic Random Access Memory) includes a switching transistor and a capacitor. The advanced microprocessing technique has realized shrinkage of the memory cell, which decreases the charge storage capacity of a memory cell. In order to solve the disadvantages of the decrease of the charge storage capacity, a COB (capacitor over bit-line) structure and an STC (stacked trench capacitor) structure have been used in constituting the memory cell. In the memory cell, a capacitor is disposed over a bit-line so as to allow the increases in the projected area and the height of the capacitor, thereby allowing the increase in the area of a capacitor electrode or electrodes.
Japanese Unexamined Patent Application, First Publication, No. 2004-221467 discloses a conventional memory cell structure that is constituted by the COB and the STC. The capacitor of the memory cell has a cylindrically shaped bottom electrode which is realized by a ruthenium film. The ruthenium film is adjacent to an inter-layer insulator of silicon oxide. It is necessary to ensure the adhesiveness between the ruthenium film and the silicon oxide film as the inter-layer insulator. In order to ensure the adhesiveness between the ruthenium film and the silicon oxide film, an adhesive layer is interposed between them. The adhesive layer can be formed by oxidizing a titanium nitride film. The adhesive layer is effective to present that during the process for forming a capacitor the ruthenium film as the bottom electrode from is peeled or removed from the silicon oxide film as the inter-layer insulator. The adhesive layer provides the adhesiveness between the bottom electrode and the inter-layer insulator, thereby preventing the above-described problems during the process for forming a capacitor.
In recent years, further shrinkage and high density integration of a memory device such as a DRAM has caused further structural complication of a capacitor and further increase in the aspect ratio thereof. The process for forming the bottom electrode includes the process for forming an extremely small contact hole with high aspect ratio in a silicon oxide film. In the process, a silicon nitride film is often used as an etching stopper. The present inventors investigated the problem about the adhesiveness between the silicon nitride film as the etching stopper and the bottom electrode film. The adhesive layer of titanium nitride provides the adhesiveness between the silicon oxide film and the bottom electrode. However, the adhesive layer of titanium nitride does not ensure the adhesiveness between the silicon nitride film and the bottom electrode. The process for forming the capacitor includes a heat treatment which may cause the peeling between the silicon nitride film and the bottom electrode, thereby deforming the bottom electrode. The deformed bottom electrode may cause increased leakage of current of the capacitor. The process for forming the capacitor also includes a wet etching process using an etchant. The peeling between the silicon nitride film and the bottom electrode by the heat treatment may cause the etchant to be drawn into the interface between the silicon nitride film and the bottom electrode, thereby causing the bottom electrode to be inclined or removed.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved semiconductor device and a method of forming the same. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.